Quote Originally Posted by dbasupuser
(Physical read/Consistent Gets)db file sequential read is where it is spending most times. We have increased the db_buffer_cache almost 1 & 1/2 and still planning to increase, since memory is not an issue on this Box.
Then your execution plans are using poor indexes, either because that's all they've got to work with (no correct indexes) or the data distribution makes CBO believe other indexes are better.

Increasing buffer pool will not help it search poor indexes any better.

If you've got specific queries/bus fcns performing poorly, As Davey23uk said - trace those fcns - and see what it's doing. This identifies the specific sql. Use explain plan on that to see why. Then see what you can do to influence that specific sql to get a better plan.